1. Technical Field
The present invention relates to a method of manufacturing a valve sleeve, and particularly to a method of manufacturing a valve sleeve for use in a hydraulic power steering gear of a vehicle.
2. Description of the Prior Art
A hydraulic power steering gear for a vehicle includes a valve sleeve and valve core located coaxially within the valve sleeve. Upon relative rotation between the valve sleeve and valve core, fluid flow is directed from a power steering pump through the valve core and valve sleeve (i) to one of a pair of fluid assist chambers in a power assist motor and (ii) from the other one of the pair of fluid assist chambers of the power assist motor to a reservoir.
The valve sleeve typically has a plurality of axially extending grooves in an inner surface of the valve sleeve. Adjacent axially extending grooves in the inner surface are separated by an axially extending land. Each of the grooves are closed at axially opposite ends by seal lands of the valve sleeve. The seal lands have a radius equal to the radius of the axially extending lands. The seal lands have a close fit with the valve core to restrict axial flow of fluid from between the valve sleeve and valve core.
Methods of making valve sleeves are disclosed in U.S. Pat. Nos. 4,419,877 and 4,614,014. In U.S. Pat. No. 4,419,877 a tubular member is provided having a plurality of axially extending grooves in its inner surface. The grooves extend completely through the axially opposite end surfaces of the tubular member. The ends of the grooves are closed by bringing punches having concave faces into forceful engagement with the opposite axial end surfaces of the tubular member. Material is displaced radially inwardly by the punches to form a continuous annular bead of material at each axial end surface of the tubular member. The displaced material extends radially inwardly of the inner surface of the valve sleeve and closes the ends of the grooves. A portion of the displaced material is then machined away to establish the finished diameter of the inner surface of the valve sleeve and the axial extent of the seal lands.
In U.S. Pat. No. 4,614,014 a tubular member is provided having a plurality of axially extending grooves in its inner surface. The grooves extend completely through axially opposite end surfaces of the tubular member. An annular groove is machined in the each of end surfaces of the tubular member radially outwardly of the inner surface of the tubular member. A tool forcefully engages a wall of each annular groove to displace material of the end surfaces radially inwardly. The displaced material extends radially inwardly of the inner surface of the tubular member. The tool engages and displaces material only in an area adjacent each groove. The sleeve is then bored to remove portions of the displaced material and to establish the finished diameter of the inner surface of the valve sleeve and the axial extent of the seal lands.
The seal lands on the valve sleeves made according to these known methods are formed by (i) displacing material of the valve sleeve radially inwardly and (ii) removing a portion of the displaced material by machining. Thus, the seal land area has an axially extending dimension which results from these steps.